Free Astronomy Magazine September-October 2024

49 SEPTEMBER-OCTOBER 2024 ASTRO PUBLISHING T his artist’s concept shows the nova system HM Sagittae (HM Sge), where a white dwarf star is pulling material from its red giant companion. This forms a blazing hot disk around the dwarf, which can un- predictably undergo a spontaneous thermonuclear explosion as the infall of hydrogen from the red giant grows denser and reaches a tipping point. These fireworks between companion stars are fascinating to astronomers by yielding insights into the physics and dynamics of stellar evolution in binary systems. [NASA, ESA, Leah Hustak (STScI)]